Described below is an arrangement for infrared spectroscopy in attenuated total reflection (ATR infrared spectroscopy).
In infrared spectroscopy, a molecular spectrum of a sample to be spectroscopically analyzed is obtained by using light whose wavelength range lies in the infrared. In inorganic and organic substances, the infrared radiation is typically absorbed by excitation of mechanical oscillations of one or more molecules. Excitation of rotational levels is also possible in the case of relatively small molecules. Since the oscillation or rotation energies as quantum-mechanical eigenstates are characteristic of a molecule, the molecule and its bonds can be deduced from the absorption spectrum. Infrared spectroscopy therefore allows quantitative structural clarification of substances, the identification of which is carried out with the aid of a reference spectrum.
One particular version of infrared spectroscopy is infrared spectroscopy in attenuated total reflection (ATR infrared spectroscopy). In this case, according to the related art, the infrared radiation is guided by total reflection in a reflection element. If such total reflection takes place at an interface between a sample and a reflection element, then the infrared light enters the sample exponentially at the position of the total reflection. This entering evanescent wave interacts with the sample, so that frequency ranges characteristic of the sample are absorbed. The absorbed frequency ranges are therefore then absent in the spectrum of the totally reflected light beam. Advantageously, substances or samples which are opaque for the infrared radiation used, and for which a transmission spectrum cannot therefore be obtained, can also be spectroscopically analyzed in ATR infrared spectroscopy. furthermore, ATR infrared spectroscopy is also suitable for liquid and/or powdered samples. For many applications, besides the spectral information, local resolution, i.e. imaging of the sample, is also necessary in ATR infrared spectroscopy. According to the related art, however, such imaging is affected by strong noise. Particularly for applications of ATR infrared spectroscopy in surgery, however, a high signal strength and therefore a highly sharp differentiation of healthy and diseased tissue is desirable. Another disadvantage of known ATR infrared spectroscopy when used in surgery is that the samples are always surrounded by liquids, in particular by water and/or blood. The surrounding water, however, leads to strong absorption in the spectral range of from about 4 μm to 10 μm, which is superimposed on the actual measurement signal of the tissue.